Study suggests dolphins use coral mucus as medicine

VSHimpanzees have learned to eat plants that kill or eliminate parasitic worms. Wood ants ward off pathogens by incorporating resin into their nests. Various species of Mexico City birds embed cigarette butts in their nests to prevent tick infestations. Capuchin monkeys bite centipedes and rub the toxins they produce into their fur, keeping mosquitoes away. The animal kingdom is replete with examples of animals that know, either innately or by observing their parents or peers, how to use plants and other animals for medicinal purposes. Dolphins could be another example, according to a study published today (19 May) in iScience.

The study makes two main findings: that a pod of Indo-Pacific bottlenose dolphins (Tursiops aduncus) repeatedly and deliberately rub against specific corals and sea sponges, and that when these invertebrates are agitated, they release mucus containing cocktails of bioactive compounds with antimicrobial, hormonal and cytotoxic properties. Researchers extrapolate that dolphins have learned to use certain organisms to treat skin conditions or infections.

Study co-author Angela Ziltener, a wildlife biologist at the University of Zurich, says The scientist that she started observing this group of dolphins in 2009 and that she has since been “adopted”: during her dives, the dolphins adopt a seemingly normal behavior in her presence, seem to be comfortable with the fact that Ziltener will be close to their young, and will return to her depth after surfacing to get some air and swim at her speed. During some dives, Ziltener says, she noticed group members rubbing against particular types of corals and sponges, and she wanted to figure out what was going on.

The dolphins take turns swimming against the coral, potentially for therapeutic purposes.


Ziltener teamed up with colleagues to conduct a detailed chemical analysis of bioactive compounds secreted by gorgonian coral (Rumphella aggregate), coral leather (Sarcophyton sp.), and sponges (Ircinia sp.), three invertebrates against which dolphins selectively rub their bellies, fins and faces. For this part of the study, study co-author Gertrud Morlock, an analytical chemist and food scientist at the Justus-Liebig University of Giessen in Germany, made the most of centimeter cuttings of coral and sponge that the team was allowed to take – and felt comfortable taking from the reef. To do this, Morlock performed planar separation chromatography, a technique that breaks up a compound and individually tests for its active ingredients, which allowed the team to perform multiple analyzes on the properties of each of their limited samples.

“We wanted to get an overview of the effects” of the bioactive compounds, says Morlock The scientist. “We used ten different tests.”

The team found 17 different metabolites in the samples, which they believe are secreted in the mucus of the invertebrates. Some were already known, providing proof-of-concept validation for their technique, Morlok says; others were new to science. Samples of all three species contained antibacterial compounds, while leather coral also included some hormones.

Ziltener tells The scientist that they have no evidence that these compounds actually help dolphins as a cure or prophylactic, which is why the study cannot say with certainty that the animals are self-medicating. And taking skin samples from dolphins to find the answer isn’t possible under regulations protecting dolphins — and could result in Ziltener being thrown out of the pod.

See “Chimpanzees seem to treat the wounds of others with the help of insects”

Animal self-medication experts who spoke to The scientist about the new study agrees with Ziltener that the research does not provide conclusive evidence for self-medication. Jaap de Roode, an Emory University biologist who is currently writing a book on animal self-medication, notes that the paper does not show that dolphins actually receive a medical benefit from coral. Still, he says he “wouldn’t be at all surprised” if that were the case. “It’s certainly plausible.” He adds that some of the identified antibacterial compounds could, theoretically, be explored for potential clinical use.

Wesleyan University biologist Michael Singer, who also did not work on the study, agrees the self-medication hypothesis is plausible, but suggests other possibilities are that the dolphins are simply scratching a itchiness or use mucus to camouflage their appearance or smell.

A dolphin with a fungal infection on its dorsal fin


Even though dolphins do heal themselves, Ziltener says it’s unclear if the animals are aware of doing so, or if they just crave something that feels good on their skin, similar to how humans do. use hand cream. “It’s of course hard to say,” she said. “But because the substances come into contact with the skin” and because the dolphins deliberately seek out and press against specific species of invertebrates, the animals are likely seeking the effects of the specific compounds. She adds that the dolphins will perform the behavior regardless of whether they are alone or with the pod, sometimes rubbing against the coral when they first wake up or before sleeping, as if they were a nightly routine.

One conclusion Ziltener draws is that the application of coral and sponge secretions is a learned behavior. The newborn dolphins hang back and watch the older members of the group, healthy and sick, as they line up and swim again and again against the specific corals, sometimes grabbing sponges in their mouths and shaking them, coating thus their face of bioactive mucus. . When the calves first try it, they seem shy and uncertain, Ziltener says, but eventually they understand and mirror the behavior of their elders, pressing their fins and torso against the corals and rubbing their faces against the sponges. . Learned self-medication is common in intelligent animals, says Jessica Abbott, an evolutionary biologist at Lund University in Sweden, who also did not work on the study but has published a study on self-medication. insects. Other animals, such as insects, seem to innately self-medicate, de Roode adds.

See “Wildborn Doctors”

In the future, Ziltener plans to continue observing dolphins in hopes of better understanding this behavior, including determining whether it varies between sexes or between individuals.

Abbott adds that she would like to know if dolphins around the world exhibit similar behavior or if it is an isolated cultural phenomenon within the pod observed by Ziltener. For his part, de Roode says he’s thrilled the phenomenon of animal self-medication is getting more attention, especially since most examples occur in terrestrial life.

“I think it’s exciting that as the field grows, people are starting to interpret these behaviors in different ways,” de Roode says, “whereas 20 years ago people maybe looked at these dolphins and said, ‘I have no idea what they’re doing.'”